The present invention relates to a dehydrogenation catalyst and process using the catalyst, especially a platinum-chromium-lithium-alumina catalyst.
Catalytic dehydrogenation processes are well known and are discussed in general by Kearby in Chapter 10, pages 453-491, of Catalysis, Vol. III, edited by P. H. Emmett, Reinhold Publishing Corporation (1955). Exemplary dehydrogenation reactions are:
(1) Propane.fwdarw. propene+ H.sub.2 PA1 (2) butene.fwdarw. butadiene+ H.sub.2 PA1 (3) ethylbenzene.fwdarw. styrene+ H.sub.2 PA1 (4) butane.fwdarw. butadiene+ 2H.sub.2
Typical dehydrogenation temperatures are between 400.degree. and 800.degree. C., and typical pressures are 0.1 to 100 atmospheres.
The Catalysis Chapter 10 reference cited above summarizes various dehydrogenation catalysts, for instance at pages 463 and 475, including the well-known chromia-alumina catalyst. According to the Beeck reference (Nature, 136, page 1028 (1935)) discussed in the Catalysis Chapter 10 reference referred to above, appreciably less severe dehydrogenation conditions were required when components such as oxides of chromium, vanadium, iron, zinc or nickel were added to activated alumina used for dehydrogenating isobutane in the presence of small amounts of water. Also, of the materials tested by Beeck, the chromia-on-alumina was reported to give the best results.
U.S. Pat. No. 2,956,030 discloses that typical commercial chromia-alumina dehydrogenation catalysts are prepared using activated alumina having a surface area of about 80 square meters per gram. The alumina is impregnated with chromic acid, dried, and calcined to obtain a finished catalyst having about 20 weight percent chromia and a surface area of about 50-60 square meters per gram. According to U.S. Pat. No. 2,956,030 an improved catalyst is provided using a particular type of alumina (gamma alumina) and an alkali metal content controlled to lie in the well-defined range of about 0.15 to 0.5% alkali metal oxide by weight of the catalyst. Also somewhat higher surface area alumina is used as the catalyst support, preferably 150 m.sup.2 /g or more.
U.S. Pat. No. 2,870,084 discloses the use of a chromia-platinum-alumina catalyst for aromatizing a naphtha feed. The catalyst used is a coprecipitated alumina-chromia catalyst having 70-82 mol percent alumina, 30-18 mol percent chromia, and 0.001 to 1.0 mol percent platinum oxide or palladium oxide.
U.S. Pat. No. 3,554,901 discloses the use of a chromium-platinum-palladium-alumina catalyst for aromatizing hydrocarbons. The catalyst is prepared by impregnating a carrier such as silica or alumina or silica-alumina with 0.1 to 1.0 weight percent platinum, 0.1 to 1.0 percent palladium, and 5 to 25 percent chromium oxide.
U.S. Pat. No. 3,780,129 discloses the use of a chromic oxide-nickel-lithium-alumina catalyst for dehydrogenation of hydrocarbons, as, for example, dehydrogenation of n-butane to obtain butenes and butadiene, and dehydrogenation of isopentane to obtain isoamylenes and isoprene. According to the example in U.S. Pat. No. 3,780,129, the catalyst was prepared by mixing commercially available alumina-chromia catalyst with nickel nitrate, lithium nitrate, and additional inert alpha-alumina followed by drying and calcining. The claimed catalyst consists essentially of 1-40% by weight chromium oxide, 0.01-0.1% nickel oxide, 0.1-10% lithium oxide, and the remainder alumina.
The use of alkali metals in dehydrogenation catalysts has been disclosed, for example, in U.S. Pat. No. 3,126,426: platinum group metal on alumina with a large amount, preferably over 5 weight percent, of alkali metals such as potassium; U.S. Pat. No. 3,119,883: zinc oxide plus iron, tin, or bismuth plus less than 1 weight percent alkali metal; U.S. Pat. Nos. 3,363,023: chromia plus magnesia plus alkali metal on an alumina support; and 3,439,061, Group VIII noble metal sulfide on a silica support.
The use of four-component dehydrogenation catalysts has been disclosed in several patents to Haensel and Block, for example U.S. Pat. Nos. 3,293,319; 3,291,755; 3,291,855; 3,391,218; 3,448,165; 3,448,166; and 3,682,838. According to U.S. Pat. No. 3,293,319 the dehydrogenation catalyst for dehydrogenating saturated hydrocarbons comprises about 0.01-1.5 weight percent lithium, from about 0.05 to 5 weight percent Group VIII metal component, and a further metal component selected from arsenic, antimony, and bismuth. Typically an alumina support is used for the catalyst.
U.S. Pat. No. 3,531,543 discloses a dehydrogenation catalyst which comprises a Group VIII noble metal, tin, a support such as alumina, and a neutralizing component such as lithium.
Japanese pat. appln. No. 084972 discloses a dehydrogenation catalyst containing platinum and chromium and platinum-chromium polyphthalocyanine on a porous support, which support does not contain lithium.